Ferrite carrier core material and ferrite carrier for electrophotographic developer, methods for manufacturing these, and electrographic developer using the ferrite carrier

A ferrite carrier core material for an electrophotographic developer, wherein:

• (1) a ferrite composition contains 0.5 to 2.5% by weight of Sr;
• and a presence amount of Sr—Fe oxides satisfies the following conditional expression:
• 0<a weight of a Sr ferrite/a total weight of all Sr—Fe oxides≦0.8 [Expression 1]
• provided that the total weight of all Sr—Fe oxides=the Sr ferrite+the Sr—Fe oxides other than the Sr ferrite;
• (2) in the distribution in the number of the shape factor SF-2, the number of particles of 100 or more and less than 105 is 40% by number or more;
• that of 105 or more and less than 110 is 5 to 40% by number;
• that of 110 or more and less than 120 is 20% by number or less;
• that of 120 or more is 10% by number or less;
• and that of 130 or more is 5% by number or less;
• (3) the BET specific surface area is 0.15 to 0.30 m2/g;
• (4) the average particle diameter D50 in measurement by a laser diffraction type particle size distribution analyzer is 20 to 35 μm;
• and
• (5) the magnetization by VSM measurement when a magnetic field of 1K·1000/4π·A/m is impressed is 50 to 65 Am2/kg.